1. Field of the Invention
The present invention is concerned with novel chlorophenylalkoxyalkyl compounds, their manufacture, liquid crystalline mixtures which contain these compounds and their use for electro-optical purposes.
2. Description
Liquid crystals are used primarily as dielectrics in indicating devices, since the optical properties of these substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well-known to a person skilled in the art and can be based on various effects. Examples of such devices are cells having dynamic scattering, DAP cells (deformation of aligned phases), guest/host cells, TN cells having a twisted nematic structure, STN cells ("super-twisted nematic"), SBE cells ("super-birefringence effect") and OMI cells ("optical mode interference") and recently, having regard to the interest in actively addressed liquid crystal applications, also TFT cells (thin film transistor). The most common indicating devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.
The liquid crystal materials must have a good chemical and thermal stability and a high stability towards electric fields and electro-magnetic radiation. They should have a low viscosity and in the cells should give short response times, low threshold potentials and a high contrast. Furthermore, at usual operating temperatures they should should have a suitable mesophase, for example a nematic, cholesteric or chiral tilted smectic phase. Further properties such as the electrical conductivity, the dielectric anisotropy and the optical anisotropy must fulfil different requirements depending on the type of cell and field of application. For example, materials for cells having a twisted nematic structure should have a positive dielectric anisotropy and an electrical conductivity which is as low as possible. In addition to the general interest in liquid crystal materials having a high optical anisotropy there has recently been an increased in materials having a low optical anisotropy, especially for actively addressed liquid crystal indicators, e.g. in the case of TFT applications (thin film transistor) in television sets.
In order to optimize the properties liquid crystals are usually used as mixtures of several components. It is therefore important that the components have a good miscibility with one another.